1. Field of the Invention
The present invention relates to a coating structure and a method for manufacturing the same, and particularly relates to an extreme low resistivity light attenuation anti-reflection coating structure and a method for manufacturing the same.
2. Description of the Related Art
It is well known that the conventional layer structure for an anti-reflection optical coating has a general principle. This general principle is that the surface layer of the optical coating should be a material that scores low on the refractive index such as SiO2, scoring 1.46 on the refractive index, or MgF2, scoring 1.38 on the refractive index. However, when we apply the metal base anti-reflection coating on a display screen to create a high EMI shielding effect for a computer monitor, or low reflection glass for an LCD or a PDP, there are some bottlenecks in the process for high volume mass production. The basic reason for this is that the protective layer for example SiO2 or MgF2 of the optical layer structure is nature porous in microstructure and allow the H2O vapor diffuse into the inside low resistivity metal thin layer to change the electric and optical characteristic of the layer system.
On the other hand, in the general design rule for an anti-reflection coating, the first layer deposited on the substrate surface is a material with a high score on the refractive index (hereafter referred to as H), which is then followed by a second layer that is a material with a low score on the refractive index (hereafter referred to as L). The basic design rule for the conventional anti-reflection coating is that there is a layer structure such as HLHL or HLHLHL. In a simple case, if the materials of H are ITO and the materials of L are SiO2, the 4-layered structure is glass/ITO/SiO2/ITO/SiO2. Because ITO is a transparent conductive material, the multi-layer coating of this layer structure has electrical conductivity of less than 100 Ω/square, and can be used as an EMI shielding and/or electric static discharge when the conductive coating layer is bonded to the ground. However, when the electronic circuit move to more fast speed and more powerful function. A significant request for extreme low resistivity, namely ≦0.6 Ω/square, were ask for provide better function in EMI (Electronic magnetic Interference) shielding. Conventional multi-layer ITO coating have good performance in resistivity range of several Ω/square. However, below 1.0 Ω/square will largely increase the difficulty of mass production and result in a very high cost in final application.
On the other hand, although thin metal layer has good conductivity in electrical characteristic, but the metal also has many limitation in the application to form a multi optical layer system.
A well know phenomenon of thin film metal layer is the durability of thin metal layer. Once water vapor diffuse into the surface and contact with the thin metal layer, a oxidation process will occur spontaneously and finally change the chemical property of thin metal layer and significantly change the electrical and optical characteristic of the optical layer system. A design of special compound layer was used as a surface protect layer for this invention. This surface protective layer were compose of Titanium oxide, Silicon dioxide and Aluminum oxide. The protective layer is a effective diffusion barrier to prevent the water vapor diffuse from the surface into inner metal layer.